JPWO2019163320A1 - Power tool control circuit - Google Patents

Abstract

The power tool control circuit according to the present invention is a power tool control circuit including a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor. It is provided with a current detecting means for detecting the current flowing through the PWM inverter circuit, and limits the current flowing through each switching element of the permanent magnet synchronous motor and the PWM inverter circuit to a predetermined current limit value when braking the permanent magnet synchronous motor. At the same time, by switching the low-side or high-side switching element of the PWM inverter circuit, the induced electromotive voltage of the permanent magnet synchronous motor is boosted and regenerated into the battery.

Description

The present invention relates to, for example, a control circuit and a control method for a power tool using a permanent magnet synchronous motor, and a power tool.

In general, power tools such as drill drivers and impact tools are designed to improve operability and responsiveness by braking when stopped.

As an example, in Patent Document 1, in an electric tool using a three-phase brushless motor as a drive source, when the rotation of the three-phase brushless motor is reduced or stopped, the terminals of the three-phase brushless motor are short-circuited. A so-called short-circuit brake (short-circuit braking) that generates a braking force has been proposed.

Further, in Patent Document 2, the brake current can be passed through a diode provided in parallel with the switching element, and the switching element is turned on at a timing when the brake current flowing through the switching element is in a decreasing direction. A braking device for an electric tool, which is characterized by switching from a diode to an off state, has been proposed.

Special Fair 6-104000 Gazette Japanese Patent No. 6155175

However, the methods of Patent Documents 1 and 2 described above have the following problems.
(1) The current flowing through the switching element cannot be controlled during braking, and the element is damaged.
(2) An element having a large current rating is required according to the maximum current flowing during braking.
(3) Braking takes time because the inertial energy during tool rotation is consumed mainly by the electrical resistance of the motor winding. In addition, the motor generates a large amount of heat.
(4) Braking force, braking time, etc. cannot be controlled.

An object of the present invention is to solve the above problems and to provide a power tool control circuit and control method, and a power tool, which are cheaper and more reliable than those of the prior art.

The power tool control circuit according to the first invention is a power tool control circuit including a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor.
The control circuit
A current detecting means for detecting the current flowing through the PWM inverter circuit is provided.
When braking the permanent magnet synchronous motor, the current flowing through the permanent magnet synchronous motor and the PWM inverter circuit is limited to a predetermined current limit value.

In the power tool control circuit, the PWM inverter circuit is provided between the permanent magnet synchronous motor and the battery.
The control circuit boosts the induced electromotive voltage of the permanent magnet synchronous motor by switching the low-side or high-side switching element of the PWM inverter circuit during braking of the permanent magnet synchronous motor, and regenerates the battery. It is characterized by doing.

Further, in the control circuit of the power tool, the control circuit is characterized in that the current limit value is changed according to the operation mode of the power tool.

The method for controlling a power tool according to the second invention is as follows.
A power tool control method executed by a power tool control circuit including a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor.
The control circuit determines a current detection step for detecting the current flowing through the PWM inverter circuit, and the control circuit determines the current flowing through the permanent magnet synchronous motor and the PWM inverter circuit when the permanent magnet synchronous motor is braked. It is characterized by including a current limiting step that limits the current limit value of.

The power tool according to the third invention is
An electric tool including a battery, a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor.
It is characterized by being provided with a control circuit for the power tool.

Therefore, according to the power tool control circuit and control method according to the present invention, it is possible to reduce the element cost and improve the reliability of the tool by controlling so as to limit the element current during braking. Further, by regenerating the inertial energy into the rechargeable battery 5, the braking time can be shortened. In addition, the heat generation of the motor can be reduced, and the continuous use time of the tool can be extended.

It is a block diagram which shows the structural example of the power tool which concerns on one Embodiment of this invention. It is a block diagram which shows the detailed configuration example 1 of the PWM inverter circuit 2 of FIG. It is a block diagram which shows the detailed configuration example 2 of the PWM inverter circuit 2 of FIG. It is a table which shows the commutation pattern example 1 with respect to the PWM inverter circuit 2 in the normal operation mode and the braking operation mode by the motor control device 10 of FIG. It is a table which shows the commutation pattern example 2 with respect to the PWM inverter circuit 2 in the normal operation mode and the braking operation mode by the motor control device 10 of FIG. The simulation results of the electric tool shown in FIG. 1 include (a) gate control signal, (b) motor rotation speed, (c) motor current detection value Imval and battery regeneration current Ib, and (d) motor current Iu, Iv, It is a timing chart of Iw and (e) battery voltage Vdc.

FIG. 1 is a block diagram showing a configuration example of a power tool according to an embodiment of the present invention. In FIG. 1, the electric tools according to the embodiment are, for example, a motor 1 which is a permanent magnet synchronous motor, a PWM inverter circuit 2, a gear 3, a chuck 4, a rechargeable battery 5, a capacitor 6, and a motor control device 10. And to configure. Here, the motor control device 10 includes a current detection unit 11, a current calculation unit 12, an overcurrent detection unit 51, a speed control unit 52, a current control unit 53, and a gate control unit 20. ..

FIG. 2 is a block diagram showing a detailed configuration example 1 of the PWM inverter circuit 2 of FIG. In FIG. 2, the PWM inverter circuit 2 is composed of, for example, six switching elements Q1 to Q6, such as MOSFETs, and three current detection resistors 7A, 7B, 7C (having resistance values Rx, Ry, Rz). .. The voltages of the current detection resistors 7A, 7B, and 7C are input to the current detection unit 11 of FIG. 1 and converted into current values flowing through each phase of the PWM inverter circuit. Further, the gate control signals G1 to G6 from the gate control unit 20 of FIG. 1 are applied to the gates of the switching elements Q1 to Q6. The diodes D1 to D6 connected in antiparallel to the switching elements Q1 to Q6 are parasitic diodes of the switching elements Q1 to Q6 and the like.

The embodiment of the PWM inverter circuit 2 in FIG. 2 is a so-called three-phase PWM bridge with three shunts, but the present invention is not limited to this, and the current on the DC side can be generated by one current detection resistor as shown in FIG. It is also applicable to the PWM inverter circuit 2 of the one-shunt three-phase PWM bridge to be detected. In the detailed configuration example 2 of FIG. 3, the element current of the switching element can be obtained by detecting the peak value of the current flowing through the current detection resistor 7A, and the battery current can be obtained by detecting the average value of the current flowing through the current detection resistor 7A. ..

In the motor control device 10 according to the present embodiment, the instantaneous current of the current supplied to the PWM inverter circuit 2 and a predetermined calculated current are detected to protect the switching elements Q1 to Q6, the circuit, and the rechargeable battery 5. Details will be described later.

In FIG. 1, the DC voltage from the rechargeable battery 5 is supplied to the PWM inverter circuit 2 via the capacitor 6. The PWM inverter circuit 2 PWM-modulates the supplied DC voltage with the six gate drive signals G1 to G6 from the gate control unit 20, converts it into an AC voltage, and outputs it to the motor 1. Here, the rotation of the motor 1 is transmitted to the chuck 4 of the electric tool via the gear 3. The gate control unit 20 includes motor rotation position signals Hu, Hv, Hw from Hall elements 41 to 43 provided in the motor 1, PWM signals from the current control unit 53, and a gate block from the overcurrent detection unit 51. Based on the signal, the speed detection value and the gate drive signals G1 to G6 are generated.

The voltage detected by the current detection resistors 7A, 7B, and 7C is output to the current detection unit 11, and the current detection unit 11 converts the voltage into the corresponding current value to calculate the non-inverting input terminal of the comparator 13 and the current. Output to unit 12. The current calculation unit 12 smoothes the vicinity of the peak values of the currents Ix, Iy, and Iz flowing in each phase of the PWM inverter circuit, and outputs the current to the subtractor 25.

The overcurrent detection unit 51 includes a comparator 13 and a maximum current signal generator 14. The comparator 13 compares the instantaneous current signal from the current detection unit 11 with the maximum current value from the maximum current signal generator 14, generates a gate block signal from the comparison result, and outputs the gate block signal to the gate control unit 20. To do. When the instantaneous current exceeds the maximum current value, the gate control unit 20 immediately stops driving the PWM inverter circuit 2 to protect the switching element.

The speed control unit 52 includes an absolute value calculator 30, a speed target value generator 21, a subtractor 22, a PI controller 23 that performs proportional integration control with respect to the motor speed, and a current limiter 24. To do. The absolute value calculator 30 calculates the absolute value of the speed detection value from the gate control unit 20 and outputs it to the subtractor 22. The subtractor 22 subtracts the absolute value of the speed detection value from the speed target value from the speed target value generator 21, and outputs the subtraction result to the PI controller 23. The PI controller 23 performs proportional integral control with respect to the motor speed based on the input subtraction result, and outputs a current target value for the control to the subtractor 25 via the current limiter 24. Here, the current limiter 24 prevents overcurrent in advance and protects the circuit and the rechargeable battery 5 by limiting the current target value corresponding to the speed target value within a predetermined value.

The current control unit 53 includes a subtractor 25, a PI controller 26, a limiter 27, a comparator 28, and a triangular wave generator 29. The subtractor 25 subtracts the average current signal from the current calculation unit 12 from the current target value signal indicating the current target value, and outputs the signal of the current control value of the subtraction result to the PI controller 26. The PI controller 26 performs proportional integral control with respect to the current control value, and outputs the control signal to the non-inverting input terminal of the comparator 28 via the limiter 27. Here, the limiter 27 controls the amplitude value of the PWM signal output by the comparator 28 within a predetermined value. The comparator 28 compares the control signal from the limiter 27 with the triangular wave from the triangular wave generator 29 to generate a PWM signal for driving the motor 1 by PWM modulation and output it to the gate control unit 20. ..

The gate control unit 20 generates six gate drive signals G1 to G6 based on the motor rotation position signal from the Hall element, the PWM signal, and the gate block signal, and outputs the six gate drive signals G1 to G6 to the PWM inverter circuit 2. It controls the operation of the circuit 2.

FIG. 4 is a table showing example 1 of a commutation pattern for the PWM inverter circuit 2 in the normal operation mode and the braking operation mode by the motor control device 10 of FIG.

In FIG. 4, in the normal operation mode, the gate control unit 20 selectively turns on the switching elements Q2, Q4, and Q6 in sequence, and at the same time, gates to the switching elements Q1, Q3, and Q5 with a half cycle delay. By PWM-modulating the control signals G1, G3, G5, the motor 1 is rotated at a predetermined speed.

On the other hand, when the motor is normally stopped by, for example, the user returning the trigger lever, a stop signal is output from the trigger lever 60 to the gate control unit 20. At this time, the gate control unit 20 immediately shifts from the normal operation mode to the braking operation mode, turns off the high-side switching elements Q1, Q3, and Q5, and turns off the gate control signals G2 to the low-side switching elements Q2, Q4, and Q6. , G4, G6 are PWM-modulated to decelerate and stop at a predetermined speed while braking the motor 1. At the same time, the gate control signals G2, G4, and G6 to the low-side switching elements Q2, Q4, and Q6 are PWM-modulated so as to limit the current flowing through the motor 1 and the switching elements Q2, Q4, and Q6 to a predetermined limit value. , The current flowing through the switching element during braking can be suppressed.

In the present embodiment, the current of each switching element Q2, Q4, Q6 on the low side of the PWM inverter circuit 2 is detected, and the current flowing through the motor 1 and the switching elements Q2, Q4, Q6 during braking is limited to a predetermined limiting current value. Control to do. At the time of braking, the induced electromotive force of the motor 1 is boosted by switching the low-side switching elements Q2, Q4, and Q6, and the rechargeable battery 5 is regenerated. Therefore, as shown in FIG. 4, the commutation pattern of the switching element is switched according to the usage status of the power tool.
The commutation pattern shown in FIG. 4 is an example, and the present invention is not limited to this. For example, as in the commutation pattern example 2 shown in FIG. 5, the commutation pattern of the low-side and high-side switching elements can be used. The low-side switching element may be turned off in the braking operation mode, and the high-side switching element may be PWM-controlled.

FIG. 6 shows the simulation results of the electric tool of FIG. 1, which includes (a) gate control signal, (b) motor rotation speed, (c) motor current detection value Imval and battery regeneration current Ib, and (d) motor current Iu. , Iv, Iw, and (e) timing chart of battery voltage Vdc. In FIG. 6, for convenience of illustration, a portion where the waveform changes in a complicated manner is represented by hatching.

As is clear from FIG. 6, the motor 1 that is constantly rotating during normal operation decelerates and stops at a constant speed during braking. The motor current detection value Imval is limited to a predetermined current limit value Imref during braking. It can be seen that the battery voltage Vdc rises during braking, the regenerative current Ib flows through the rechargeable battery 5, and the inertial energy is regenerated.

As described above, the present embodiment has the following unique effects.
(1) By controlling and limiting the current of the switching element, the element cost can be reduced and the reliability of the tool can be improved.
(2) Braking time can be shortened by regenerating the inertial energy into the rechargeable battery 5. In addition, the heat generation of the motor 1 can be reduced, and the continuous use time of the tool can be extended.
(3) Tool protection and operability can be improved by changing the current limit value Imref according to the operating condition of the power tool.

In the above embodiments, for example, a rotary power tool of a drill driver has been described, but the present invention is not limited to this, and can be applied to an impact type power tool.

In the above embodiment, the motor control device 10 may be mainly composed of hardware or software.

1 Motor 2 PWM Inverter circuit 3 Gear 4 Chuck 5 Rechargeable battery 6 Capacitors 7A, 7B, 7C Current detection resistance 10 Motor control device 11 Current detection unit 12 Current calculation unit 13 Comparator 14 Maximum current signal generator 20 Gate control unit 21 Speed Target value generator 22 Subtractor 23 PI controller 24 Current limiter 25 Subtractor 26 PI controller 27 Limiter 28 Comparator 29 Triangular wave generator 30 Absolute value calculator 41-43 Hall element 51 Overcurrent detector 52 Speed control unit 53 Current control unit 60 Trigger lever D1 to D6 Backflow prevention diode G1 to G6 Gate control signal Ix, Iy, Iz Detected current value Q1 to Q6 Switching element

FIG. 2 is a block diagram showing a detailed configuration example 1 of the PWM inverter circuit 2 of FIG. In FIG. 2, the PWM inverter circuit 2 is composed of, for example, six switching elements Q1 to Q6 such as MOSFETs and three current detection resistors 7A, 7B, and 7C (having resistance values Rx, Ry, and Rz). To. The voltages of the current detection resistors 7A, 7B, and 7C are input to the current detection unit 11 of FIG. 1 and converted into current values flowing in each phase of the PWM inverter circuit 2 . Further, the gate control signals G1 to G6 from the gate control unit 20 of FIG. 1 are applied to the gates of the switching elements Q1 to Q6. The diodes D1 to D6 connected in antiparallel to the switching elements Q1 to Q6 are parasitic diodes of the switching elements Q1 to Q6 and the like.

In FIG. 1, the DC voltage from the rechargeable battery 5 is supplied to the PWM inverter circuit 2 via the capacitor 6. The PWM inverter circuit 2 PWM-modulates the supplied DC voltage with the six gate control signals G1 to G6 from the gate control unit 20, converts it into an AC voltage, and outputs it to the motor 1. Here, the rotation of the motor 1 is transmitted to the chuck 4 of the electric tool via the gear 3. The gate control unit 20 includes motor rotation position signals Hu, Hv, Hw from Hall elements 41 to 43 provided in the motor 1, PWM signals from the current control unit 53, and a gate block from the overcurrent detection unit 51. Based on the signal, the speed detection value and the gate control signals G1 to G6 are generated.

The voltage detected by the current detection resistors 7A, 7B, 7C is output to the current detection unit 11, and the current detection unit 11 converts the voltage into the corresponding current values Ix, Iy, Iz and non-inverts the comparator 13. Output to the input terminal and the current calculation unit 12. The current calculation unit 12 smoothes the vicinity of the peak values of the currents Ix, Iy, and Iz flowing in each phase of the PWM inverter circuit 2 , and outputs the current to the subtractor 25.

The overcurrent detection unit 51 includes a comparator 13 and a maximum current signal generator 14. The comparator 13 compares the instantaneous current signal from the current detection unit 11 with the maximum current value from the maximum current signal generator 14, generates a gate block signal from the comparison result, and outputs the gate block signal to the gate control unit 20. To do. When the instantaneous current exceeds the maximum current value, the gate control unit 20 immediately stops driving the PWM inverter circuit 2 and protects the switching elements Q1 to Q6 .

The gate control unit 20 generates six gate control signals G1 to G6 based on the motor rotation position signals from the Hall elements 41 to 43 , the PWM signal, and the gate block signal, and outputs them to the PWM inverter circuit 2. Controls the operation of the PWM inverter circuit 2.

On the other hand, for example when the user normally stops the motor 1 in operation such as returning the trigger lever 60, the stop signal from the trigger lever 60 to the gate controller 20 is outputted. At this time, the gate control unit 20 immediately shifts from the normal operation mode to the braking operation mode, turns off the high-side switching elements Q1, Q3, and Q5, and turns off the gate control signals G2 to the low-side switching elements Q2, Q4, and Q6. , G4, G6 are PWM-modulated to decelerate and stop at a predetermined speed while braking the motor 1. At the same time, the gate control signals G2, G4, and G6 to the low-side switching elements Q2, Q4, and Q6 are PWM-modulated so as to limit the current flowing through the motor 1 and the switching elements Q2, Q4, and Q6 to a predetermined limit value. , The current flowing through the switching elements Q2, Q4 and Q6 during braking can be suppressed.

In the present embodiment, the current of each switching element Q2, Q4, Q6 on the low side of the PWM inverter circuit 2 is detected, and the current flowing through the motor 1 and the switching elements Q2, Q4, Q6 during braking is limited to a predetermined limiting current value. Control to do. At the time of braking, the induced electromotive force of the motor 1 is boosted by switching the low-side switching elements Q2, Q4, and Q6, and the rechargeable battery 5 is regenerated. Therefore, as shown in FIG. 4, the commutation pattern of the switching elements Q1 to Q6 is switched according to the usage status of the power tool.
The commutation pattern shown in FIG. 4 is an example, and the present invention is not limited to this. For example, as in the commutation pattern example 2 shown in FIG. 5, commutation of low-side switching elements Q2, Q4, and Q6. The pattern and the commutation pattern of the high-side switching elements Q1, Q3 and Q5 are exchanged, the low-side switching elements Q2, Q4 and Q6 are turned off in the braking operation mode, and the high-side switching elements Q1, Q3 and Q5 are PWMed. You may control it.

As is clear from FIG. 6, the motor 1 rotating at a constant speed during normal operation decelerates and stops at a constant speed during braking, and the motor current detection value Imval is limited to a predetermined current limit value Imref during braking. and being, the battery voltage Vdc increases during braking, regenerative current Ib flows through the rechargeable battery 5, it is found and the inertial energy is regenerated.

As described above, the present embodiment has the following unique effects.
(1) By controlling and limiting the currents of the switching elements Q1 to Q6 , the element cost can be reduced and the reliability of the tool can be improved.
(2) Braking time can be shortened by regenerating the inertial energy into the rechargeable battery 5. In addition, the heat generation of the motor 1 can be reduced, and the continuous use time of the tool can be extended.
(3) Tool protection and operability can be improved by changing the current limit value Imref according to the operating condition of the power tool.

Claims (5)

A control circuit for an electric tool including a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor.
The control circuit
A current detecting means for detecting the current flowing through the PWM inverter circuit is provided.
A control circuit for an electric tool, which limits the current flowing through the permanent magnet synchronous motor and the PWM inverter circuit to a predetermined current limit value when the permanent magnet synchronous motor is braked. The PWM inverter circuit is provided between the permanent magnet synchronous motor and the battery.
The control circuit boosts the induced electromotive voltage of the permanent magnet synchronous motor by switching the low-side or high-side switching element of the PWM inverter circuit during braking of the permanent magnet synchronous motor, and regenerates the battery. The control circuit for an electric tool according to claim 1, wherein the control circuit is provided. The power tool control circuit according to claim 1 or 2, wherein the control circuit changes the current limit value according to the operation mode of the power tool. A power tool control method executed by a power tool control circuit including a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor.
A current detection step in which the control circuit detects a current flowing through the PWM inverter circuit,
The control circuit includes a current limiting step that limits the current flowing through each switching element of the permanent magnet synchronous motor and the PWM inverter circuit to a predetermined current limit value when the permanent magnet synchronous motor is braked. How to control the power tool. An electric tool including a battery, a permanent magnet synchronous motor, a plurality of switching elements, and a PWM inverter circuit for driving the permanent magnet synchronous motor.
A power tool comprising the control circuit for the power tool according to any one of claims 1 to 3.

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